[Pro34]neuropeptide Y selectively identifies postjunctional-mediated actions of neuropeptide Y in vivo in rats and dogs

Anaesthetised rats and dogs were used to study the pre- and postjunctional actions of neuropeptide Y (NPY) and [Pro34]NPY simultaneously. Increases in arterial blood pressure indicated postjunctional actions and both NPY and [Pro34]NPY elicited these. Change in pulse interval evoked by stimulation of the cut peripheral end of the right vagus nerve, indicated prejunctional action of the peptides: NPY caused prolonged attenuation of vagal action in rats and dogs but [Pro34]NPY did not attenuate vagal action in rats or dogs.

C-terminal KDEL-modified cystatin C is retained in transfected CHO cells

The significance of a C-terminal tetrapeptide, Lys-Asp-Glu-Leu (KDEL), as a retention signal for the endoplasmatic reticulum was studied using cystatin C, a general thiol protease inhibitor, as the reporter protein. Clones of CHO cells were analyzed after stable transfection with eukaryotic expression vectors encoding either cystatin C, KDEL extended cystatin C, or cystatin C extended with a control sequence. It is concluded that cystatin C with the KDEL tetrapeptide as a C-terminal extension is retained intracellularly without apparent accumulation of the molecule.

Structure-function studies on neuropeptide Y and pancreatic polypeptide--evidence for two PP-fold receptors in vas deferens

The biological effects of neuropeptide Y (NPY), rat pancreatic polypeptide (rPP), hybrid analogs of NPY and PP, and C-terminal fragments of NPY were studied in the field-stimulated rat vas deferens model. The results were correlated with peptide binding experiments in Y1 and PP receptor assays on rat PC-12 cells and Y2 receptors on porcine hippocampal membranes. NPY and rPP inhibited the electrically induced contractions in the vas deferens with an IC50 of 25 and 22 nM respectively. However, in contrast to NPY, rPP could not totally block muscle activity. The inhibitory action of the long C-terminal fragment of NPY, NPY-(19-36) and NPY-(11-36), indicated that NPY acts through a Y2 receptor in the vas deferens. The structural basis for the differential recognition of NPY and PP by Y2 receptors and partly also by PP receptors, could be defined with hybrid analogs of PP and NPY. The analogs, [Ile31,Gln34]PP and [Leu31,Pro33]NPY reacted in the vas deferens preparation in accordance with their relative potency in the Y2 and PP receptor assays. [Ile31,Gln34]PP, which bound to the Y2 receptor like NPY, was also able to block the part of the contractile response which was resistant to rPP. It is concluded that in the vas deferens, PP-fold peptides act through two types of receptors: Y2 and PP, and that residues in the C-terminal part of the molecules determine the differential recognition of the peptides by these receptor types.

Biosynthesis of peptide precursors and protease inhibitors using new constitutive and inducible eukaryotic expression vectors

A series of expression vectors has been constructed as based on the pML derivative of pBR322. The eukaryotic transcription units employ various promoters followed by polycloning sites for 3-9 commonly used restriction enzymes and are completed by the SV40 polyadenylation sequence. In 4 of the vectors, designed for co-transfection or transient expression studies, only a single transcription unit containing either a constitutive or an inducible promoter was incorporated. The human ubiquitin (UbC) promoter was used as a strong constitutive promoter, while the mouse metallothionein promoter and the promoter of the long terminal repeats of the mouse mammary tumor virus were used as inducible promoters. Another vector contained an additional transcription unit encoding a eukaryotic selection marker, the neomycin resistance encoding gene. The vectors were used in CHO cells and in neuroendocrine CA77 cells to synthesize peptide precursors, protease inhibitors and a protease. It is shown that these vectors are very efficient for the constitutive and inducible expression of nucleotide sequences in both transient and stable transfections of eukaryotic cells.

The antiparallel pancreatic polypeptide fold in the binding of neuropeptide Y to Y1 and Y2 receptors

Neuropeptide Y (NPY) belongs to the pancreatic polypeptide fold (PP-fold) family of regulatory peptides. Analysis of circular dicroic spectra of NPY showed that it has a high degree of secondary structure in aqueous solution which is in agreement with the globular, folded crystal structure of PP. Using three different approaches with synthetic peptides, we have probed the importance of the PP-fold structure in the interaction of NPY with two types of binding sites, Y1 and Y2 receptors. First, stepwise construction of the NPY molecule from the C-terminal amidated end, showed that although C-terminal fragments encompassing most of the long alpha-helix reacted reasonably well with the Y2 receptor, both Y1 and Y2 receptors required the presence of both ends of the PP-fold for full activity. Second, perturbation of the PP-fold by substitution with a helix-breaking proline residue, resulted in the loss of recognition of the N-terminal segment of the molecule by both types of receptors. Finally, a hybrid analog was constructed in which the essential, but by itself inactive, C-terminal segment of NPY was joined with the PP-fold motif of PP. This segment of PP is only 43% homologous to the similar motif in NPY, and most of the common residues cluster in the hydrophobic core of the fold. Nevertheless, the hybrid analog reacted with almost full potency on the Y2 receptors. It is concluded that the antiparallel PP-fold is of structural importance for the receptor binding of NPY, and that its main function is to present the combined C- and N-terminal segments of the molecule to the receptors.

Production of gastrin-releasing peptide-(18-27) and a stable fragment of its precursor in small cell lung carcinoma cells

The production and postsecretory stability of gastrin-releasing peptide (GRP) and the C-terminal part of the GRP precursor were studied in small cell lung cancer cell lines using RIAs developed against these two parts of the precursor. In three otherwise different cell lines (NIC-H345, NIC-H69, and NIC-H510), similar chromatographic patterns of mainly GRP-(18-27) and some GRP-(14-27) along with large fragments of the C-terminal counterpart of the precursor were found to be stored in the cells. In tissue culture medium, gel filtration chromatography indicated that postsecretory limited proteolysis of the GRP precursor fragments occurred. The amount of accumulated immunoreactivity varied among the three cell lines and between the two parts of the precursor. In medium in which only low amounts of GRP immunoreactivity accumulated, the radiolabeled GRP was degraded rapidly. When incubated with plasma, GRP-(14-27) disappeared within a few hours, whereas the C-terminal precursor fragments were stable. It is concluded that the postsecretory stability of peptides excised from the GRP precursor in small cell lung cancer cells varies under tissue culture conditions, but epitopes in the C-terminal part of the precursor are more stable in plasma than the small GRP peptides and, thus, may serve as a better indicator than GRP itself for expression of the GRP precursor in cancer cells.

Partial processing of the neuropeptide Y precursor in transfected CHO cells

The activation of regulatory peptides by post-translational modification of their biosynthetic precursors is generally thought to occur only in neuroendocrine cells. We have selected clones of Chinese hamster ovary cells, a non-neuroendocrine cell line, which were transfected with a eukaryotic expression vector coding for the precursor for neuropeptide Y. Although the majority of the immunoreactive NPY was found in the form of pro-NPY, some degree of intracellular proteolytic processing of the precursor occurred in all clones. Part of the intracellular NPY immunoreactivity was even correctly amidated. Extracellular degradation of pro-NPY in the tissue culture medium generated immunoreactivity which corresponded in size to NPY. It is concluded that precursor processing can occur in non-neuroendocrine cells both as a biological process within the cells and as apparent processing, degradation in the tissue culture medium.

Y1 receptors for neuropeptide Y are coupled to mobilization of intracellular calcium and inhibition of adenylate cyclase

Two types of binding sites have previously been described for neuropeptide Y (NPY), called Y1 and Y2 receptors. The intracellular events following Y1 receptor activation was studied in the human neuroblastoma cell line SK-N-MC. Both NPY and the specific Y1 receptor ligand, [Leu31,Pro34]-NPY, caused a rapid and transient increase in the concentration of free calcium in the cytoplasm as measured by the fluorescent probe, Fura-2. The effect of both peptides was independent of extracellular calcium as addition of EGTA or manganese neither changed the size nor the shape of the calcium response. The calcium response to NPY was abolished by pretreatment with thapsigargin, which can selectively deplete a calcium store in the endoplasmic reticulum. Y1 receptor stimulation, by both NPY and [Leu31,Pro34]NPY, also inhibited the forskolin-stimulated cAMP production with an EC50 of 3.5 nM. There was a close relation between the receptor binding and the cellular effects as half-maximal displacement of [125I-Tyr36]monoiodoNPY from the receptor was obtained with 2.1 nM NPY. The Y2-specific ligand NPY(16-36)peptide had no effect on either intracellular calcium or cAMP levels in the SK-N-MC cells. It is concluded that Y1 receptor stimulation is associated with both mobilization of intracellular calcium and inhibition of adenylate cyclase activity.

[Leu31, Pro34]neuropeptide Y: a specific Y1 receptor agonist

Two types of binding sites have previously been described for 36-amino acid neuropeptide Y (NPY), called Y1 and Y2 receptors. Y2 receptors can bind long C-terminal fragments of NPY-e.g., NPY-(13-36)-peptide. In contrast, Y1 receptors have until now only been characterized as NPY receptors that do not bind such fragments. In the present study an NPY analog is presented, [Leu31, Pro34]NPY, which in a series of human neuroblastoma cell lines and on rat PC-12 cells can displace radiolabeled NPY only from cells that express Y1 receptors and not from those expressing Y2 receptors. The radiolabeled analog, [125I-Tyr36] monoiodo-[Leu31, Pro34]NPY, also binds specifically only to cells with Y1 receptors. The binding of this analog to Y1 receptors on human neuroblastoma cells is associated with a transient increase in cytoplasmic free calcium concentrations similar to the response observed with NPY. [Leu31, Pro34]NPY is also active in vivo as it is even more potent than NPY in increasing blood pressure in anesthetized rats. It is concluded that [Leu31, Pro34]NPY is a specific Y1 receptor agonist and that the analog or variants of it can be useful in delineating the physiological importance of Y1 receptors.

Expression and precursor processing of neuropeptide Y in human and murine neuroblastoma and pheochromocytoma cell lines

The synthesis and processing of the precursor for neuropeptide Y (NPY) were studied in 16 human and murine neuroendocrine cell lines. Eight of the cell lines, NS-20Y, PC12, LA-N-5, CHP-234, SMS-KCNR, SH-SY5Y, SMS-KCN, and BE(2)-M17, produced sufficient quantities to permit chromatographic characterization of the NPY immunoreactivity. Although the cell lines varied in the amount of NPY they produced, both within and between cell lines, they displayed a relatively constant pattern of posttranslational modifications. In contrast to observations in tumor extracts (M. M. T. O'Hare and T. W. Schwartz, Cancer Res., 49: 7010-7014, 1989), all cell lines studied contained a substantial amount of the intracellular NPY in the form of the unprocessed propeptide, 57% (range, 33-72%) as characterized by both gel filtrations (32 experiments in 8 cell lines) and "in vitro conversion" with endoproteinase Lys-C. In the majority, 4 of 6 cell lines studied, almost all of the NPY, which by size corresponded to the mature 36-amino acid form, was amidated as assessed by isoelectric focusing and by a radioimmunoassay specific for the COOH-terminal amide group of the peptide. Both the propeptide and smaller molecular forms of NPY were secreted from the cell cultures; however, proteolytic degradation in the tissue culture medium prevented a detailed, meaningful characterization of these peptides. It is concluded that many neuroendocrine cell lines, especially those derived from human neuroblastomas, express the NPY gene; the cells display a partly impaired dibasic processing capacity but they generally amidate the products efficiently.

Expression and precursor processing of neuropeptide Y in human pheochromocytoma and neuroblastoma tumors

The expression of the potent vasoactive peptide neuropeptide Y (NPY) was studied in 16 clinically and/or histologically diagnosed human pheochromocytomas and 3 human neuroblastoma tumors. All tumors contained NPY in concentrations ranging from 21 pmol/g of tissue, similar to that found in normal adrenal tissue, to 91,000 pmol/g (median, 1,700 pmol/g). Three control tumors of Cushing's type did not contain NPY. An almost total proteolytic processing of pro-NPY to normal NPY was observed in the tumors (median, 93%; range, 72-100%). A positive correlation between the processing efficiency and the NPY content was also observed. The small amount of pro-NPY found in the tumors was characterized by "in vitro conversion" with endoproteinase Lys-C. In the tumor extracts, the majority of the NPY immunoreactivity, corresponding in size to the NPY standard, also behaved like synthetic NPY by high performance liquid chromatography and isoelectric focusing. As assessed by both its elution position in isoelectric focusing and its reaction with an antiserum specific for the COOH-terminal amidated sequence, the peptide produced by the tumors was found to be efficiently amidated, a modification which is essential for the biological activity of NPY. It is concluded that although only a subset of chromaffin cells express NPY, a very high number of pheochromocytomas and neuroblastomas produce correctly amidated and thus biologically active NPY in large amounts, and that this is of potential importance for tumor-related cardiovascular symptoms and for autocrine stimulation of tumor cells.

Y2-type receptors for peptide YY on renal proximal tubular cells in the rabbit

By means of primary cell cultures and luminal and basolateral membrane vesicles a single class of high-affinity binding sites for peptide YY (PYY), a member of the pancreatic polypeptide (PP)-fold family of peptides, was identified on the vascular side of the tubular epithelium in the proximal convoluted tubule of rabbit kidney. The binding of mono-iodinated radiolabeled PYY was inhibited equally well by PYY and neuropeptide Y (NPY), whereas the potency of the third member of the family, PP, was 10(5) times lower. Because NPY immunoreactive nerves in the mammalian kidney are confined to vascular smooth muscle cells and the juxtaglomerular apparatus, we propose that the physiological ligand for this binding site is blood-borne PYY. The kidney PYY receptor was sensitive to guanine nucleotides and could be classified as belonging to the Y2-subtype of NPY receptors, thus resembling in its binding characteristics the hippocampal NPY receptor. The high amounts of Y2-type PYY receptors present on the proximal tubule cell in rabbit kidney should permit studies on the functions and mechanisms of actions of PYY.

Elevated plasma concentrations of C-flanking gastrin-releasing peptide in small-cell lung cancer

Many small-cell lung cancers (SCLCs) produce gastrin-releasing peptides (GRPs) (mammalian bombesin) but the plasma concentration of GRP is rarely elevated, possibly because of its rapid elimination. We developed a radioimmunoassay for the C-terminal flanking peptide of proGRP and measured its concentration in plasma from 71 patients with SCLC, in 27 healthy subjects and in 49 patients with other diseases including lung carcinomas. In addition, we studied the molecular size of immunoreactive C-flanking peptide in two SCLC cell lines and in plasma from SCLC patients. The concentration of immunoreactive C-flanking peptide in normal subjects and in control patients did not exceed 10 pmol/L and 26 pmol/L, whereas 72% of the SCLC patients had C-flanking peptide concentrations above 10 pmol/L. In patients with extensive disease (n = 35) the median concentration was 71 pmol/L (range, 10 to 940). ProGRP C-flanking peptide levels paralleled the clinical course in 12 patients. The molecule(s) responsible for the immunoreactivity had a molecular size of about 8 to 10 kd in both patient plasma and tumor cell lines, suggesting that the measured peptide(s) represented major fragment(s) if not the entire C-flanking peptide of proGRP. Thus this peptide(s) seems to be a useful marker for SCLC.

Release of PYY from pig intestinal mucosa; luminal and neural regulation

The localization, molecular nature and secretion of Peptide YY (PYY), a putative gut hormone belonging to the Pancreatic Polypeptide family of peptides, was studied in pigs. Immunoreactive PYY was identified in a population of endocrine cells in the mucosal epithelium of the pig ileum. Release of PYY was observed in isolated perfused pig ileum in response to luminal stimulation with glucose and vascular administration of the neuropeptide gastrin-releasing peptide (GRP). Electrical stimulation of the vagus nerve supply to the distal small intestine in intact anaesthetized pigs resulted in release of PYY into the circulation. Stimulation of the splanchnic nerves did not affect the basal release of PYY. PYY-immunoreactivity extracted from ileal tissue or released to plasma or perfusate from the ileum was indistinguishable from synthetic porcine PYY by gel filtration and reverse phase HPLC. It is concluded that the secretion of PYY in the pig ileum may be regulated not only by nutritional luminal factors, but also by postsynaptic parasympathetic nerves.

Neuropeptide Y in the human female genital tract: localization and biological action

The distribution, localization, and smooth muscle effects of neuropeptide Y (NPY) were studied in the human female genital tract. High concentrations of NPY immunoreactivity were demonstrated in the uterine artery, the ovary, the fallopian tube, cervix, and the vagina. The NPY immunoreactivity was confined to nerve fibers. The highest density of nerve fibers was observed in relation to blood vessels, although some NPY-immunoreactive nerves were also seen close to nonvascular smooth muscle. The NPY-immunoreactive material throughout the genital tract was identical to synthetic amidated human NPY with regard to size, hydrophobicity, and charge as evaluated by gel filtration, high-performance liquid chromatography, and isoelectric focusing. NPY (10(-10) to 10(-6) M) exerted a direct vasoconstrictory effect on small arteries dissected from the cervix and an additive effect of NPY and norepinephrine responses was observed. Exogenous NPY did not have a direct effect on nonvascular smooth muscle specimens from the fallopian tube or the myometrium. The close relation between NPY-immunoreactive nerves and blood vessels, the presence of NPY-immunoreactive material identical to amidated synthetic human NPY, and the vasoconstrictory effects of NPY indicate that NPY is involved in the regulation of the blood flow in the human female genital tract.

Regional distribution of neuropeptide Y and its receptor in the porcine central nervous system

The regional distribution of neuropeptide Y (NPY) immunoreactivity and receptor binding was studied in the porcine CNS. The highest amounts of immunoreactive NPY were found in the hypothalamus, septum pellucidum, gyrus cinguli, cortex frontalis, parietalis, and piriformis, corpus amygdaloideum, and bulbus olfactorius (200-1,000 pmol/g wet weight). In the cortex temporalis and occipitalis, striatum, hippocampus, tractus olfactorius, corpus mamillare, thalamus, and globus pallidus, the NPY content was 50-200 pmol/g wet weight, whereas the striatum, colliculi, substantia nigra, cerebellum, pons, medulla oblongata, and medulla spinalis contained less than 50 pmol/g wet weight. The receptor binding of NPY was highest in the hippocampus, corpus fornicis, corpus amygdaloideum, nucleus accumbens, and neurohypophysis, with a range of 1.0-5.87 pmol/mg of protein. Intermediate binding (0.5-1.0 pmol/mg of protein) was found in the septum pellucidum, columna fornicis, corpus mamillare, cortex piriformis, gyrus cinguli, striatum, substantia grisea centralis, substantia nigra, and cerebellum. In the corpus callosum, basal ganglia, corpus pineale, colliculi, corpus geniculatum mediale, nucleus ruber, pons, medulla oblongata, and medulla spinalis, receptor binding of NPY was detectable but less than 0.5 pmol/mg of protein. No binding was observed in the bulbus and tractus olfactorius and adenohypophysis. In conclusion, immunoreactive NPY and its receptors are widespread in the porcine CNS, with predominant location in the limbic system, olfactory system, hypothalamoneurohypophysial tract, corpus striatum, and cerebral cortex.

Binding of monoiodinated neuropeptide Y to hippocampal membranes and human neuroblastoma cell lines

Monoiodinated radioligands of the homologous 36-amino acid peptides, neuropeptide Y (NPY) and peptide YY, were prepared by reverse phase high performance liquid chromatography with isocratic elution. [125I-Tyr1]- and [125I-Tyr36]monoiodoNPY bound equally well to a single class of high affinity binding sites on synaptosomal membranes prepared from porcine hippocampus (Kd = 1.0 X 10(-10) M) whereas iodine substitution in Tyr27, for example, partly interfered with the receptor binding. The receptors on the hippocampal membranes did not distinguish between neuropeptide Y and peptide YY either in their monoiodinated or in their unlabeled forms. Six out of twelve human neuroblastoma cell lines had high affinity binding sites for monoiodinated NPY ranging from 2 to 145 X 10(3) sites per cell. The NPY binding to three of the cell lines, SMS-MSN, SMS-KAN, and CHP-234 was of relatively high affinity (Kd = 1.3 to 6.1 X 10(-10) M), and, as in the hippocampal membranes, the long C-terminal fragment, NPY(13-36)peptide was also a relatively potent ligand for these receptors. Two other neuroblastoma cell lines, MC-IXC and CHP-212, expressed NPY receptors characterized by a lower affinity (Kd = 4.8 and 24.6 X 10(-9) M) and negligible cross-reactivity with the C-terminal fragment. It is concluded that monoiodinated radioligands of the tyrosine-rich neuropeptide Y can be prepared and that receptors for these ligands in two apparently different subtypes are found on a series of human neuroblastoma cell lines.

Y1 and Y2 receptors for neuropeptide Y

By using monoiodinated radioligands of both intact neuropeptide Y (NPY) and of a long C-terminal fragment, NPY13-36, two subtypes of binding sites, which differ in affinity and specificity, have been characterized. The Y1 type of binding site, characterized on a human neuroblastoma cell line, MC-IXC, and a rat pheochromocytoma cell line, PC-12, binds NPY with a dissociation constant (Kd) of a few nanomolar but does not bind NPY13-36. The Y2 type of binding site, characterized on porcine hippocampal membranes and on another human neuroblastoma cell line, SMS-MSN, is of higher affinity and binds both NPY and NPY13-36. None of the binding sites distinguish between NPY and the homologous peptide YY (PYY). It is concluded that NPY/PYY-binding sites occur in two subtypes which may represent two types of physiological receptors.

Tyrosylation and purification of peptides for radioiodination

A simple method for tyrosylation, purification and subsequent radioiodination of peptides which lack suitable acceptor groups for iodine substitution is presented. The reagent, tert.-butyloxycarbonyl-L-tyrosine N-hydroxysuccinimide ester, was used for conjugation to the amino groups of peptides. The derivatization was performed with relatively large amounts of reagents to ensure quantitative reactions. The derivatized peptides were purified by reversed-phase high-performance liquid chromatography or by gel filtration. Subsequent radioiodination was performed with sodium [125I]iodide and the sparingly soluble tetrachlorodiphenylglycouril as the oxidative agent to minimize possible oxidative damage to the peptides. The radiolabelled peptides were subsequently purified by isocratic high-performance liquid chromatography.

Effect of amino acid analogs on the processing of the pancreatic polypeptide precursor in primary cell cultures

Amino acid analogs, which can be incorporated into nascent peptide chains were used in cultures of endocrine cells from canine pancreas to study the effect on processing of the metabolically labeled precursor for pancreatic polypeptide. Analogs for basic amino acids, canavanine, and aminoethylcysteine prevented the di-basic processing of the prohormone. The polar leucine analog, beta-hydroxyleucine, only partially perturbed the function and cleavage of the signal peptide but efficiently and unexpectedly blocked the dibasic cleavage of the prohormone. Other nonbasic amino acid analogs, beta-hydroxynorvaline and azetidine-2-carboxylic acid, which only could be incorporated into the prohormone at a distance from the processing site, also prevented dibasic cleavage of the prohormone. Although there are no phenylalanine residues in the prohormone, analogs for this amino acid, fluoro-phenylalanine and particularly phenylserine, could also block the processing of the prohormone at the dibasic site. This effect was prevented by addition of a small quantity of phenylalanine. It is concluded that amino acid analogs can interfere with precursor processing through altering both the primary and the secondary structure of the precursor but also through incorporation into cosynthesized protein(s) which are necessary for the precursor processing.

Release of NPY in pig pancreas: dual parasympathetic and sympathetic regulation

Several lines of evidence have connected neuropeptide Y (NPY), a 36-residue polypeptide, to the sympathetic division of the autonomic nervous system. We studied the localization, the molecular characteristics, and the release of NPY and norepinephrine (NE) in the porcine pancreas. Immunohistochemical investigations revealed that NPY nerves around blood vessels were likely to be of adrenergic nature, whereas NPY-immunoreactive fibers close to exocrine and endocrine cells may originate from local ganglia also containing VIP (vasoactive intestinal peptide) and PHI (peptide histidine isoleucine). Electrical stimulation of the splanchnic nerve supply to the isolated perfused pig pancreas resulted in a corelease of NPY and NE into the venous effluent. Stimulation of the vagal nerves caused a sevenfold larger release of NPY without affecting the NE secretion. Characterization of the NPY immunoreactivity in the pancreatic tissue and in the venous effluent by gel filtration, high-performance liquid chromatography, and isoelectric focusing showed that the immunoreactive NPY was indistinguishable from synthetic porcine NPY. It is concluded that, although NPY is associated with sympathetic perivascular neurons, the majority of the pancreatic NPY-containing nerve fibers are likely to belong to the parasympathetic division of the autonomic nervous system.